In passive optical waveguide networks, couplers serve as optical components for distributing the light signals from incoming optical waveguides to output optical waveguides. Couplers of this type comprise a transparent element which is connected to optical waveguides on the light-entry and light-exit sides. In addition to couplers produced by bonding or melting transparent moldings together with optical waveguides, couplers are also known which are produced by twisting optical waveguide bundles and stretching them at the twist point (Agarwal, Fiber Integr. Optics 6 (1), 27-53, 1987).
However, the production of composite couplers of this type is complex and expensive; in addition, the transmission attenuation of such known couplers is difficult to reproduce, which means that the performance varies by more than 1 dB between the various output fibers.
Furthermore, couplers are known in which fiber bundles comprising polymeric optical waveguides are melted by means of a shrink tube (DE-A-37 37 930) or optical waveguides are joined at the end faces of a cylindrical mixing zone (R.D. Codd, SAE/IEEE, Internat. Congress of Transportation Electronics, 1984).
A process for deforming an optical waveguide bundle by impression of a die is described in DE-A-39 19 263, which is not a pre-priority publication. The mold and die can be heated here, for example, by warming in a bath.
A further possibility comprises using high-frequency electromagnetic radiation for direct heating of the optical waveguides (DE-A-39 19 263).
The essential disadvantage of all the production methods is the complex process steps, which, as in, for example, the biconical taper process (Agarwal, Fiber Integr. Optics 6 (1), 27-53, 1987), either permit only piece-by-piece manufacture or mean that production automation is only possible using expensive specialized machines.
Furthermore, couplers of this type in which the optical waveguides are joined in the mixing zone always have relatively high optical losses; in addition, couplers produced by the biconical taper process are mechanically unstable.